X-ray microscopes are powerful tools in the nano-inspection of materials owing to their ultra-high resolution at the molecular level. However, the focusing efficiency of binary zone plate lenses as key components in such probes is merely 5% in practice, hindering their application in advanced scientific research. Although kinoform zone plate lenses are in principle supposed to possess high efficiency beyond binary ones, little progress has been reported so far due to the shortage of both a theoretical calculation approach and greyscale lithography for generating fine three-dimensional (3D) kinoform zones of the lenses. This paper reports our theoretical work for a modified beam propagation method to compute the focusing performance and state-of-the-art 3D greyscale electron beam lithography for kinoform zone plate lenses. Three different zone shapes – binary, kinoform and top-flat kinoform (nicknamed the trapezoid-kinoform) – were compared both theoretically and experimentally. Theoretical calculations suggest, for the first time, that the trapezoid-kinoform zone plate gives rise to the highest focusing efficiency among the three lenses, which was proved by optical characterization of the fabricated lens with hard X-rays. As high as 40% of the focusing efficiency by Au trapezoid-kinoform lenses with resolution of 250 nm at 8 keV has been achieved, which is two times higher than that of binary zone plate lenses. The origin of the enhanced efficiency in the trapezoid-kinoform zone plate lens was explained by the joint contributions from both the refraction through the kinoform slope and the diffraction through the top flat part of the trapezoid-kinoform zone plate. Such a breakthrough in focusing efficiency sheds light on the further development of X-ray lenses with both high resolution and high efficiency.

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Applications of subwavelength grating based-polarizers for polarimetric detections are being hindered due to the limited extinction ratio. In this work, the structural effect, including the line edge roughness (LER), of the gratings on the polarizing characteristics was studied by both numerical simulations using finite difference and time domain (FDTD) method and experiments, aiming to figure out the optimal grating profile for achieving high transmittance as well as high extinction ratio. Two different configurations of the gratings, one is dual layer Au lines and the other is parabolic shaped Al lines on structured spin-on-carbon (SOC) films were systematically studied and compared. Nanofabrication of the gratings by electron beam lithography without lift-off process were conducted and optical measurements of their polarization properties demonstrate superior performance of the developed polarizers. The origin of the structural effect was explained by the local surface plasmonic modes, existing in the nano-slits in metallic gratings, which is instructive for further enhancement of the polarization performance.

X-ray microscope as an important nanoprobing tool is expected to play a powerful role in nano-inspections of materials. Despite the fast advances of high resolution focusing/imaging reported, the diffraction efficiency of existing binary zone plates as the lenses in the microscope is mostly around 5% in practice and rapidly goes down to 1-2% when the resolution approaches 10 nm, failing its applications in advanced scientific research. Zone plates with Kinoform profile are supposed to be high efficient, little progress for achieving both high resolution and high efficiency has been reported. The conflict between the resolution and the efficiency in X ray optics has become a long-lasting bottleneck in the further development of X-ray microscope. Based on our earlier success in developing high efficiency Kinoform zone plates by greyscale electron beam lithography, we proposed, in this work, a new zone plate structure by combing a dielectric Kinoform zone plate with an atomic layer deposited HfO2 zone plate to achieve high resolution focusing/imaging with high efficiency. Beam propagation method was applied in designing and optimizing Kinoform shapes of the zones, greyscale and/or binary electron beam lithography was carried out for generating both 3D Kinoform as well as rectangular zones with aspect ratio of 23/1 in dielectric resist, and finally high-quality atomic layer deposition of HfO2 was conducted to form the 15-nm wide outermost zone. Optical characterizations by an in-house developed soft X ray microscope demonstrated 15-nm resolution focusing/imaging with over 7% efficiency, which is the highest with such a resolution as far as our awareness. The origin of such an improvement behind the proposed novel lenses is interpreted by our BMP calculation results and the comparisons with existing performances by other reports in literature was discussed.